Crucible for vaporizing chemically active elements method of manufacturing the same and ion source including said crucible

ABSTRACT

The invention relates to ion sources having two ionization chambers and more particularly to chemical and heat resistant crucibles for use with said sources. The crucible in accordance with the invention is a hollow box of pyrolytic tungsten having two opposite openings in its lateral wall. The crucible is manufactured from a pyrolytic tungsten deposite made on a copper mandrel which is dissolved in an etching bath.

United States Patent [191 Kervizic et al.

[ CRUCIBLE FOR VAPORIZING CHEMICALLY ACTIVE ELEMENTS METHOD OFMANUFACTURING THE SAME AND ION SOURCE INCLUDING SAID CRUCIBLE [75]Inventors: Jacques Kervizic; Rene Masic;

Arvind Shroff; Robert Jean Wamecke, all of Paris, France [73] Assignee:Thomson-CSF, Paris, France [22] Filed: June 22, 1972 [21] Appl. No.:265,303

[30] Foreign Application Priority Data July 6, 1971 France 7124682 [52]US. Cl 313/63, 29/5272, 263/48, 3l3/l80,313/231 [51] Int. Cl. H0511 1/02[58] Field Of Search 313/63, 180, 231

[111 3,789,253 [451 Jan. 29, 1974 [56] References Cited UNITED STATESPATENTS 3,631,283 12/1971 Gautherm et a1 313/231 Primary Examinerl-l. K.Saalbach Assistant Examiner-Darwin R. Hostetter Attorney, Agent, orFirm.lohn W. Malley et a].

57 I ABSTRACT The invention relates to ion sources having two ionizationchambers and more particularly to chemical and heat resistant cruciblesforuse with said sources.

The crucible in accordance with the invention is a hollow box ofpyrolytic tungsten having two opposite openings in its lateral wall. Thecrucible is manufactured from a pyrolytic tungsten deposite made on acopper mandrel which is dissolved in an etching bath.

4 Claims, 6 Drawing Figures PAIENIEnJmsmm sum 3 0r 3 CRUCIBLE FORVAPORIZING CHEMICALLY ACTIVE ELEMENTS METHOD OF MANUFACTURING THE SAMEAND ION SOURCE INCLUDING SAID CRUCIBLE The present invention relates toion sources comprising two ionization chambers and more particularly tothe crucible associated with the second ionization chamber, the lattermaking it possible to produce ions of chemically active elements.

In ion sources, for example of the Triplasmatron type, the secondionization chamber, as described by the applicants in the US. Pat. No.3,631,283, 9th Apr. 1968, is a metal enclosure which is integral withthe first ionization chamber and which contains a reservoir or crucibleholding the elements which are to be ionised.

These crucibles are generally made of graphite, quartz or molybdenum.However, in certain cases, these materials are unsuitable and this isparticularly so if it is necessary to raise the elements which are to bevaporised, to high temperatures. One known solution consists in usingcrucibles of refractory materials, but the majority of these, in thepresence of chemically active elements such as boron, form an eutecticsystem whose melting point is very much lower than that of the materialbeing used.

The invention overcomes these drawbacks and its object is a crucible forvaporization of a chemically active elements comprising a hollow box ofpyrolytic tungsten said box having a lateral wall and bottom and topwalls said lateral wall having two openings aligned along an axiscrossing said lateral wall said chemically active elementsbeingintroduced within said box through one of said openings.

Another object of this invention is an ion source including a crucibleas aforesaid, said source comprising a first ionization chambercontaining a gas G a cathode located in said first ionization chamberfor emitting electrons, said electrons generating within said firstchamber a primary plasma due to the collisions of said electrons withparticles of said gas G a second ionization chamber containing saidcrucible and an extraction system for extracting ions obtained in saidsecond ionization chamber through the interaction of said primary plasmawith vaporized-particles of said elements, said vaporized particlesbeing produced with heating means associated with said crucible the axisof said openings being aligned with the mean path of the ion beamemerging from said first ionization chamber.

For the better understanding of the invention and to show how the samemay be carried into effect, reference will be made to the followingdescription accompanying the attached drawings in which a FIG. 1illustrates in section a crucible in accordance with the invention, thecrucible being provided with a support.

FIG. 2 illustrates a crucible attached to a support in a mannerdiffering from that shown in FIG. 1.

FIGS. 3, 4 and 5 illustrate various stages in the manufacturing of acrucible.

FIG. 6 illustrates, in section, an ion source comprising a crucibleassociated with heating means.

FIG. 1 shows a crucible C formed by a cylindrical hollow box having alateral wall I and top and bottom walls 2 and 3 made of pyrolytictungsten, the lateral wall 1 of the box being provided with two openings4 and 5 arranged opposite one another and having a common axis 6. Thebottom wall 3 of the crucible C is brazed to a support 7 of sinteredtungsten, itself integral with a tantalum tube 9, the brazing beingeffected through the medium of a refractory metal 8 such for example asniobium. It is possible to replace the support 7 of sintered tungsten bya brazed molybdenum cup 10 as FIG. 2 shows.

This crucible C can be carried out in the following four stages a.Machining a cylindrical hollow copper mandrel M having externaldimensions corresponding to the internal dimensions of the box formingthe crucible C, the mandrel M being provided with a protruding lateralsupport member 11 which is a tubular member in the chosen example, asshown in FIG. 3.

b. Depositing tungsten by pyrolysis onto said mandrel. The mandrel M isintroduced into a quartz tube around which an HLF. heating coil slides.The quartz tube is then evacuated down to a pressure of some fewmillimetres of mercury.

Hydrogen is then introduced into the quartz tube and the mandrel heatedto around 6009C. Then, tungsten hexafluoride WF is for exampleintroduced into the quartz tube, triggering the chemical reactionFluorhydric acid formed as a consequence, is then condensed out. It ispossible to use tungsten chlorides or tungsten oxychlorides as well. Itis equally possible to utilise the pyrolytic reaction of anorgano-metallic compound. The reaction is halted when the desiredthickness of tungsten deposit 12 has been produced on the mandrel M.

c. Selectively dissolving the cylindrical copper man-- drel in nitricacid. (FIG. 4).

d. And drilling a second opening 5 in the lateral wall of thecylindrical crucible C opposite the opening 4 formed by the lateralsupport-member l l of the copper mandrel when the mandrel and itssupport-member 11 have been dissolved, the openings 4 and 5 beingaligned along an axis crossing the lateral wall and being diametrallyopposite (FIG. 5). The external surface of the crucible is thenfinished.

In FIG. 6, an ion source of the Triplasmatronf type has been shown whosesecond ionization chamber 14 is equipped with a crucible C. Thiscrucible C is fixed to the tantalum tube 9. The openings 4 and 5 in thecrucible are located along the mean path of the particle beam issuingfrom the first ionization chamber 20, said beam being obtained, inoperation, by ionizationof the gas G contained in the first chamber,through the-collisions between the electrons emitted by the cathode Hand the gas particles G The device for heating the crucible C comprisesa tungsten filament l5 coiled several times. The two ends 16 and 17 ofthe filament 15 are connected to a direct voltage source which has notbeen shown in the figure. Thiskind of filament makes it'possible toraise the crucible C to a temperature greater than 2,000 C, by electronbombardment.

Trials have been carried out with an ion source comprising a cruciblecharged with amorphous boron. The results obtained are given here by wayof example the crucible being at ambient temperature, a beam current ofA formed with He ions (the first ionization chamber 20 containinghelium), was measured at the output of the ion source. On raising thetemperature of the crucible to 1,800 C, the total current at the outputof the ion source remained constant but the proportion of He ionsdecreased in favour of B ions which made up around 5 percent of thetotal current.

at around 2,000 C, with a total current still equal to 1 l0 uA, theproportion of B ions in the particle beam was 16 percent.

at 2,l50 C, the proportion of B ions was 28 percent.

finally at 2,250" C, the beam current of 150 A was obtained, essentiallycomposed of B ions (94 percent), the l-le ions making up around 5.5percent.

These extremely significant results, not hitherto attainable with theconventional means since the latter do not enable boron to be raised toa sufficiently high temperature, show the advantage which is presentedby a crucible of homogeneous pyrolytic tungsten, containing no bubblesor microscopic cracks, as described.

What we claim is: p

1. An ion source comprising a first ionization chamber containing a gasG a cathode located in said first ionization chamber for emittingelectrons, said electrons generating within said first ionizationchamber a primary plasma due to the collisions of said electrons withparticles of said gas G a-second ionization chamber; a crucible withinsaid second ionization chamber for vaporization of chemically activeelements, said crucible comprising a hollow box of pyrolitic tungsten,said box having a lateral wall and bottom and top walls, said lateralwall having two openings aligned along an axis crossing said lateralwall, said chemically active elements being introduced within said boxthrough'one of said openings and an extraction system for extractingions obtained in said second ionization chamber through the interactionof said primary plasma with vaporized particle of said elements, saidvaporized particles being produced with heating means associated withsaid crucible the axis of said openings being aligned with the mean pathof the ion beam emerging from said first ionization chamber.

2. An ion source as claimed in claim 1, wherein said chemically activeelement contained in said crucible is boron.

3. An ion source comprising a first ionization chamber containing a gasG a cathode located in said first ionization chamber for emittingelectrons, said electrons generating within said first chamber a primaryplasma due to the collisions of said electrons with particles of saidgas G a second ionization chamber; a crucible within said secondionization chamber for vaporization of chemically active elements, saidcrucible comprising a cylindrical hollow box of pyrolitic tungstenhaving a revolution axis said box having a lateral wall and bottom andtop walls, said lateral wall having two openings aligned along an axiscrossing said lateral wall, said chemically active elements beingintroduced within said cylindrical hollow box through one of saidopenings and an extraction system for extracting ions obtained in saidsecond ionization chamber through the interaction of said primary plasmawith vaporized particles of said elements, said vaporized particlesbeing produced with heating means associated with said cylindricalcrucible said axis of said openings formed in the lateral wall of saidcylindrical crucible being aligned with the mean path of the ion beamemerging from said first ionization chamber, said mean path and saidaxis being perpendicular with said revolution axis of said cylindricalcrucible.

4. An ion source as claimed in claim 3, wherein said chemically activeelement contained in said cylindrical crucible is boron.

2. An ion source as claimed in claim 1, wherein said chemically activeelement contained in said crucible is boron.
 3. An ion source comprisinga first ionization chamber containing a gas G1 ; a cathode located insaid first ionization chamber for emitting electrons, said electronsgenerating within said first chamber a primary plasma due to thecollisions of said electrons with particles of said gas G1 ; a secondionization chamber; a crucible within said second ionization chamber forvaporization of chemically active elements, said crucible comprising acylindrical hollow box of pyrolitic tungsten having a revolution axis ;said box having a lateral wall and bottom and top walls, said lateralwall having two openings aligned along an axis crossing said lateralwall, said chemically active elements being introduced within saidcylindrical hollow box through one of said openings ; and an extractionsystem for extracting ions obtained in said second ionization chamberthrough the interaction of said primary plasma with vaporized particlesof said elements, said vaporized particles being produced with heatingmeans associated with said cylindrical crucible ; said axis of saidopenings formed in the lateral wall of said cylindrical crucible beingaligned with the mean path of the ion beam emerging from said firstionization chamber, said mean path and said axis being perpendicularwith said revolution axis of said cylindrical crucible.
 4. An ion sourceas claimed in claim 3, wherein said chemically active element containedin said cylindrical crucible is boron.